Defrost control apparatus



L. L. KRUEGER DEFROST CONTROL APPARATUS July 16, 1963 Filed Sept. '6,1960 INVENTOR.

LOREN L. KRUEGER WflM ATTORNEY ,V// N\ M u m m R M O W m Q 8 I R 4 N 4 O5 X I 4/ R o QT e 9 w O P r y l M M H H l O 5 u l 2\ C 5 M 3 4 M 5 7 U 5w United States Patent 3,097,502 DEFROST CONTRtEL APPARATUS Loren L.Krueger, Hopkins, Minm, assignor to Minneapolis-Honeywell ReguiatorCompany, Minneapolis, MEHZL, a corporation of Delaware Filed Sept. 6,1966, Ser. No. 54,051 19 Ciaims. (Cl. 62-156) The present invention isconcerned with an improved system for controlling the defrostingoperation of a heat exchanger of a refrigeration apparatus which removesheat from outdoor air.

With the advent of air-to-air heat pumps which remove heat from outdoorair for heating a dwelling, the need for an improved control or controlsystem for initiating and terminating the defrosting operation has beenrecognized. When a refrigeration apparatus has an outdoor heat exchangerfor receiving heat from the outdoor air as the air flows through theheat exchanger, the outdoor air heat exchanger will tend to frost overto decrease the air flow through the heat exchanger and cut down theefiiciency of the system. When the outdoor heat exchanger becomescovered with frost and a defrosting operation is started, various meanshave been used to defrost the heat exchanger.

Presently, there is a control device on the market which has a pair oftemperature responsive bulbs connected to operate a switch to initiatethe defrost cycle. The temperature bulbs are adapted to respond to thecoil temperature and the outdoor air temperature, respectively. Whensuch a control device is used, a considerable amount of difficulty isexperienced in placing the one temperature responsive bulb in arepresentative position on the outdoor air heat exchanger. If the bulbis placed to respond to the temperature of the heat exchanger nearestthe warmest portion of the heat exchanger, the defrost cycle is oftencommenced quite late resulting in an extensive inefiicient operation ofthe heat pump. Also, if the heat exchanger temperature responsive bulbis placed close to the coldest portion of the heat exchanger, otherdifficulties become apparent.

The present invention is concerned with the use of three representativetemperatures for controlling the defrosting operation of the outdoor airheat exchanger. The defrosting operation is initiated when thetemperature difference between the outdoor air temperature and thenormally warmest portion of the heat exchanger reaches somepredetermined value, and the defrost cycle is terminated when thetemperature of the normally coldest portion of the coil reaches somepredetermined high temperature.

An object of the present invention is to provide an improved defrostcontrol system for a refrigeration apparatus having an outdoor air heatexchanger.

Another object of the present invention is to provide an improveddefrost control system for a refrigeration apparatus having an outdoorheat exchanger wherein the defrosting operation is initiated by thetemperature difference between the outdoor air and a first temperatureof a heat exchanger and the defrosting operation is terminated by apredetermined second representative temperature of the heat exchanger.

These and other objects of the present invention will become apparentupon the study of the following specification and drawings of which asingle FIGURE is a schernatic diagram of a typical refrigeration systemand a defrost control device having three temperature responsive bulbs.

Referring to the single figure, the temperature of space is changed bycirculating the air through an indoor coil or heat exchanger 11 which ispositioned in the air flow or duct system including a fan 12. The fan iscontinuously driven by a motor 13 to pull air into a return duct 14, andafter the air passes through the indoor coil, the air flows out ofsupply duct 15 into space 10. The indoor coil 11 is a part of arefrigeration apparatus 20 which is of a conventional type having amotor compressor 21, a changeover valve 22, an outdoor coil or heatexchanger 23. The system is connected so that the refrigerant flows inthe following manner: from the compressor, through a pipe 24, tochangeover valve 22, through a pipe 25, through coil 11, through arestriction 34, through a pipe 30, to lower side or normally coldestside 26 of the outdoor air heat exchanger 23, from the upper or normallywarmest side 31 of heat exchanger 23, through a pipe 32, through asecond portion of changeover valve 22, and back through a pipe 33 to theinlet side of the compressor. As connected, the refrigerant iscompressed and heat is given off as the refrigerant condenses in theindoor coil 11 to supply heat to space 10. In the heat exchanger 23, theliquid refrigerant evaporates to remove heat from the outdoor air whichis circulated through the heat exchanger by a fan 35 which is driven bymotor 36. The vaporized refrigerant then is pulled back into thecompressor through pipe 31.

Motor compressor 21 is connected to a switch 40 which is controlled by arelay 41. When the relay 41 is energized, the compressor 21 is connectedto a source of power by switch 40. Relay 41 is energized by aconventional circuit including a thermostat 42 which is located in space10. When a switch of thermostat 42 closes, the energization winding ofrelay 41 is connected through a source of power or step-down transformer43 to energize rnotor compressor 21 and deliver heat to space 1%).

Since the temperature of the outdoor coil 23 is generally quite low, andduring the season of the year when heating is needed in space 10, theoutdoor air temperature is low; coil 23 will tend to frost over. Thefrosting of the coil prevents the air flow through the coil and cutsdown the efficiency of refrigeration apparatus 20. In such refrigerationapparatuses, the defrosting of the outdoor coil can be accomplished in anumber of ways. One manner of defrosting the outdoor coil is thereversal of the refrigerant flow in the refrigeration apparatus byoperating changeover valve 22 to a position shown by the dotted lines.When solenoid 50 is energized, lever 51 is moved clockwise to rotate theplug 52 of the changeover valve to connect pipes 24 and '32, and pipes25 and 33. With the changeover valve operated in the defrostingposition, hot gas from motor compressor 21 is delivered directly toupper portion 31 of the coil 23. The outdoor coil is in effect reversedwith the indoor coil, and within a short time, the outdoor coil will beheated up sufficiently to melt all of the frost.

Solenoid 50 is connected to source of power 43 by a normally open switch54 which has a fixed contact 55 and a movable member 60. Movable member60 is engaged by an operating pin 61. When pin 61 is moved upward,solenoid 50 is energized to commence the defrosting cycle.

Switch operating apparatus 62 has a first bell crank lever 63 which isattached to a floating pivot pin 64. Pin 64- is not attached to a base.The bell crank has a first portion 65 extending to the right of pivotpin 64 and a second portion 70 extending to the left of pivot pin 64.Portion 70 is free to move between a pair of adjustable stops 71 and 72.A vertical portion 73 of hell crank 63 has an adjusting screw 74 whichcontacts an upper portion 75 of a second bell crank lever 80. Bell cranklever '80 is pivoted on pivot pin 64 and has a second portion 81extending to the right. Levers 63 and are connected by pin 64, but theassembly is free to move in one plane. A first output device 39 has anoutput member 91 to provide a movement in response to the temperature ofa bulb 92 located in the outdoor air stream. Such a unit might be aliquid filled system of a conventional type wherein upon the increase intemperature of bulb 92 a bellows expands or a diaphragm moves to pushmember 91 upward. A second output device 93 has a pin 94 which is movedupward when the temperature of a bulb 95 located adjacent the warmestside 31 or vapor line of the heat exchanger 23 increases. Members 91 and94 push upward on the lower side of portion 70' and portion 65,respectively, of hell crank 63. Another output device 100 has a pin 101which moves upward in response to the temperature of a bulb 102. Eachdevice 90, 93, and 100 have a calibration nut 110, 111, and 103,respectively. By rotating the nuts, the position of associated pins 91,94, and 101, respectively, can be set for a predetermined temperature ofbulbs, 92, 95, 102, respectively. Bulb 102 is located on the coldestside of heat exchanger 23 to respond to the temperature of the fluidline. When the temperature of bulb 102 increases, member 101 movesupward to move bell cnank 80 in a counterclockwise direction.

When bell crank 63 moves in a clockwise direction and screw 74 pushesbell crank 80 clockwise, the upper end of portion 75 will lift pin 61 toclose switch 54. Lever 80 is not restricted by pin 101 since bulb 102 iscold. A detent or cam surface 105 in upper portion 75 of the bell crankholds pin 61 upward and the bell crank 80 in the switch operating orfirst position even though bell crank 63 returns in a counterclockwisedirection.

Operation The normal operation of the refrigeration apparatus 20 isshown. Upon thermostat 42 calling for heat, relay 41 is energized toinitiate operation of the motor compressor. The hot gas is delivered tothe indoor coil 11, and upon the hot gas losing some heat, the gascondenses and the liquid passes through the restriction 34- to vaporizein outdoor coil 23. The heat of vaporization is obtained from theoutdoor air which passes through the coil. The lower end 26 of coil 23receives the liquid refrigerant and is normally the coldest portion ofthe coil.

As the liquid refrigerant enters the lower side of coil 23, theevaporation will normally take place in the lower twothirds of the coil.The vapor in the upper portion of the coil will be at a temperaturerelatively close to the temperature of the outdoor air; therefore, thetemperature of bulb 95 will be relatively close to the temperature ofbulb 92. By the proper calibration of devices 90 and 93 the positionapproximately as shown of bell crank 63 for relatively equal temperatureof bulbs 92 and 95 is selected. As frost begins to form .on coil 23, theevaporation of liquid refrigerant is not confined to the lowertwo-thirds of the coil since the heat transfer to the air in the frostedportion of the coil is cut down. As evaporation begins to take place inthe upper portion of coil 23, the temperature of bulb 95 will drop. Upona predetermined difference in the temperature of bulbs 92 and 95 beingreached as selected by screw 74, lever 63 will have moved clockwise asufiicient amount to pivot lever 80 until pin 61 is in detent 105. Theswitch 54 is then closed to initiate the defrost cycle.

Once the defrost operation is started by closing switch 54, any increasein temperature of bulb 95 has no effect upon the termination of thedefrosting operation as pin 61 is locked in the upward position by thedetent 105 on bell crank 80. In order to move the portion 75 to theleft, bell crank 80 has to be pivoted about pin 64 by an upward movementof member 101.

When the defrost operation is started and the upper portion of coil 23receives the hot gas, the gas will lose [heat by melting the frost offof coil 23. As the coil becomes free of frost, the hot gas will increasethe temperature of bulb 102, and member 101 will move upward to pivotbell crank 80 in a counterclockwise direction to 4 allow pin 61 to openswitch 54 to terminate the defrosting operation.

While the invention has been shown in one particular form, the inventionshould only be limited by the scope of the appended claims in which Iclaim:

1. In a defrost control system, a refrigeration apparatus comprising anindoor coil for delivering heat to a space, an outdoor coil forobtaining heat from outdoor air, a motor driven compressor, and meansconnecting said compressor, said indoor coil, and said outdoor coil intoa series system, said outdoor coil having a liquid conduit and a vaporconduit connected thereto whereby liquid refrigerant fiows into saidoutdoor coil through said liquid conduit and vapor refrigerant leavessaid outdoor coil through said vapor conduit after heat is obtained fromthe outdoor air, defrosting means adapted to heat said outdoor coil toremove frost from the coil by changing the flow of refrigerant in thesystem to deliver hot gas to the outdoor coil, first temperatureresponsive means responsive to the temperature of said liquid conduit,second temperature responsive means responsive to the temperature ofsaid vapor conduit, air temperature responsive means responsive to thetemperature of said outdoor air, means connecting said secondtemperature responsive means and said air temperature responsive meansto said defrosting means to initiate operation of said defrosting meanswhen the temperature difference between said vapor conduit temperatureand said air temperature reaches a selected value, and means connectingsaid first temperature responsive means to said defrosting means toterminate the operation of said defrosting means when the temperature ofthe liquid conduit reaches a selected value as hot refrigerant passestherethrough.

2. In a defrost control system, a refrigeration apparatus comprising anindoor coil for delivering heat to a space, a second coil for obtainingheat from a source of cold air, a motor driven compressor, and meansconnecting said compressor, said indoor coil, and said second coil intoa series refrigeration system, said second coil having a first portionwhich is first to receive liquid refrigerant from a conduit and a secondportion from which vapor refrigerant leaves said second coil, defrostingmeans adapted to heat said second coil to remove frost from the coil,first temperature responsive means responsive to the temperature of saidfirst portion, second temperature responsive means responsive to thetemperature of said second portion, air temperature responsive meansresponsive to the temperature of said air, means connecting said secondtemperature responsive means and said air temperature responsive meansto said defrosting means to initiate operation of said defrosting meanswhen the temperature difference between the temperature of said secondportion and said air temperature reaches a selected value, said secondportion decreasing in temperature as said coil becomes frosted, andmeans connecting said first temperature responsive means to saiddefrosting means to terminate the operation of said defrosting meanswhen the tempenature of said first portion reaches a selected value assaid defrosting means is operated.

3. In a defrost control system for a refrigeration system having acompressor, an indoor heat exchanger normally furnishing heat to a spaceand an outdoor air heat exchanger connected in a refrigerant filledseries system with defrosting apparatus for heating the outdoor heatexchanger when frost forms thereon, first responsive means having anoutput indicative of the temperature of the normally coldest portion ofsaid outdoor coil, second responsive means having an output indicativeof the temperature of the normally warmest portion of the outdoor coil,third responsive means having an output indicative of the temperature ofthe air entering the outdoor heat exchanger, means responsive to apredetermined difference in the output of said second responsive meansand said third responsive means for starting the operation of thedefrosting apparatus by reversing refrigerant fiow to said coils toremove frost from the outdoor heat exchanger,

and means responsive to the output of said first responsive means forterminating the operation of the defrosting apparatus.

4. In a defrost control system for a refrigeration system having arefrigerant compressor, and first heat exchanger and second heatexchanger connected in a series system and having defrosting apparatusfor defrosting the second heat exchanger when frost forms thereon, firstresponsive means having an output indicative of the temperature of oneportion of the second heat exchanger, second responsive means having anoutput indicative of the temperature of another portion of said secondheat exchanger, third responsive means having an output indicative ofthe temperature of the medium entering the second heat exchanger, meansresponsive to a predetermined dilference in the output of said secondresponsive means and said third responsive means for starting theoperation of the defrosting apparatus to remove frost from the secondheat exchanger, and means responsive to a predetermined output of saidfirst responsive means for stopping the operation of the defrostingapparatus.

5. In a defrosting control device for starting and stopping a defrostcycle of an outdoor air heat exchanger of a refrigeration apparatus, abase member, a first bell crank lever pivotally supported on a pivot formovement in a plane parallel to said base, a first and a secondmechanical output member engaging said bell crank on opposite sides ofsaid pivot, air temperature responsive means adapted to respond to theoutdoor air temperature, means connecting said air responsive means tosaid first output means to have an output movement indicative of outdoorair temperature, second temperature responsive means adapted to respondto the normally warmest portion of the heat exchanger, means connectingsaid second responsive means to said second output member to have anoutput indicative of the temperature of the warmest portion of said heatexchanger, a second bell crank pivotally supported on said pivot, asecond portion of said first bell crank engaging a first portion of saidsecond bell crank to move said second bell crank to a first positionwhen said output of said first output member exceeds said output of saidsecond member as the temperature of said warmest portion drops below thetemperature of the air, switch means mounted on said base, said switchbeing adapted to start the defrost cycle when said second bell crank isin said first position, locking means on said second bell crank to holdsaid second bell crank in said first position even though said firstbell crank moves away, a third output member, first temperatureresponsive means adapted to respond to the temperature of the normallycoldest portion of said heat exchanger, and means connecting said firsttemperature responsive means to said third member to have an outputindicative of temperature whereby when said output of said third memberrotates said second bell crank from said first position said defrostcycle is terminated.

6. In a defrosting control device for starting and stopping a defrostcycle of an air heat exchanger of a refrigeration apparatus, saiddefrost cycle being initiated by reversing the refrigerant flow to heatsaid air heat exchanger, a base member, a first bell crank leverpivotally attached to a pivot for movement in a plane parallel to saidbase, said bell crank having a first portion moving between a pair ofstops mounted on said base, a first and a second mechanical outputmembers engaging said bell crank on opposite sides of said pivot,temperature responsive means adapted to respond to the air temperature,means connecting said responsive means to said first output member tomove said bell crank upward upon an increase in air temperature, firsttemperature responsive means adapted to respond to the temperature ofone portion of said heat exchanger, second temperature responsive meansadapted to respond to the temperature of another portion of the heatexchanger, means connecting said second responsive means to said secondoutput memher to move said bell crank upward upon an increase intemperature, a second bell crank pivotally attached on said pivot, asecond portion of said first bell crank engaging said second bell crankto move said second bell crank to a first position when said output ofsaid first output member exceeds said output of said second member,switch means mounted on said base, said switch being adapted to startthe defrost cycle when said second bell crank is in said first position,a third output member, and means connecting said first temperatureresponsive means to said third member to move said second bell crankfrom said first position when the temperature of the one portionincreases to stop the defrost cycle.

7. In a control device, a base, a pivot pin, a first lever pivotallymounted on said pivot pin, a first and a second output means engagingsaid lever to move said lever in opposite directions about said pin,said first output means having an upward movement indicative of thetemperature of the air passing through a heat exchange coil of arefrigeration system, said second output means having an upward movementindicative of the temperature of the normally warmest portion of theheat exchanger, a switch operating lever adapted to initiate a defrostcycle by applying heat to said heat exchanger, said first lever movingsaid switch operating lever clockwise when said first output exceedssaid second output to move said switch lever to a switch operatingposition, a third output means having an output indicative of thetemperature of the normally coldest portion of the exchanger, and meansconnecting said third output means to said switch lever to move saidlever from said switch operating position to terminate the defrostcycle, when said coldest portion is warm.

8. A defrost control system for a refrigeration system wherein heat isremoved from air by a heat exchanger having a conduit for normallyreceiving liquid refrigerant and a conduit for vapor refrigerant tonormally leave the exchanger and having a heating means to heat theexchanger to defrost the heat exchanger comprising, first temperatureresponsive means responsive to the temperature of the heat exchangernearest the liquid conduit, second temperature responsive meansresponsive to the temperature of the heat exchanger nearest the conduitof the leaving vapor, third temperature responsive means responsive tothe temperature of the air, control means adapted to control the heatingdevice, means connecting said second temperature responsive means andsaid third temperature responsive means to said control means to startdefrosting the heat exchanger when the temperature of the vapor conduitexceeds the temperature of the air a predetermined amount, and meansconnecting said first temperature responsive means to said control meansto stop the defrosting of the heat exchange when the heating meansincreases the temperature of said first responsive means.

9. A defrost cycle control system for a refrigeration apparatus having aheat exchanger removing heat from air as air passes in thermal contactwith the heat exchanger, the heat exchanger receiving liquid refrigerantat a first portion and losing refrigerant vapor from a second portioncomprising, first responsive means having an output responsive to thetemperature of the first portion, second responsive means having anoutput responsive to the temperature of the second portion, thirdresponsive means having an output responsive to the temperature of theair, means connecting the outputs of said second and third responsivemeans to initiate a defrost cycle of the heat exchanger when thetemperature of the second portion exceeds the temperature of the air,and further means connecting the output of said first responsive meansto terminate the defrost cycle.

10. In a defrost control system for a refrigeration system having acompressor, an indoor heat exchanger and an outdoor air heat exchangerconnected in a refrigerant filled series system and having a defrostingapparatus for for starting the operation of the defrosting apparatus toremove frost from the outdoor heat exchanger, and means responsive to apredetermined output of said first responsive means for stopping theoperation of the de- 5 frosting apparatus.

References Cited in the file of this patent UNITED STATES PATENTS2,666,298 Jones Jan. 19, 1954

3. IN A DEFROST CONTROL SYSTEM FOR A REFRIGERATION SYSTEM HAVING ACOMPRESSOR, AN INDOOR HEAT EXCHANGER NORMALLY FURNISHING HEAT TO A SPACEAND AN OUTDOOR AIR HEAT EXCHANGER CONNECTED IN A REFRIGERANT FILLEDSERIES SYSTEM WITH DEFROSTING APPARATUS FOR HEATING THE OUTDOOR HEATEXCHANGER WHEN FROST FORMS THEREON, FIRST RESPONSIVE MEANS HAVING ANOUTPUT INDICATIVE OF THE TEMPERATURE OF THE NORMALLY COLDEST PORTION OFSAID OUTDOOR COIL, SECOND RESPONSIVE MEANS HAVING AN OUTPUT INDICATIVEOF THE TEMPERATURE OF THE NORMALLY WARMEST PORTION OF THE OUTDOOR COIL,THIRD RESPONSIVE MEANS HAVING AN OUTPUT INDICATIVE OF THE TEMPERATURE OFTHE AIR ENTERING THE OUTDOOR HEAT EXCHANGER, MEANS RESPONSIVE TO APREDETERMINED DIFFERENCE IN THE OUTPUT OF SAID SECOND RESPONSIVE MEANSAND SAID THIRD RESPONSIVE MEANS FOR STARTING THE OPERATION OF THEDEFROSTING APPARATUS BY REVERSING REFRIGRANT FLOW TO SAID COILS TOREMOVE FROST FROM THE OUTDOOR HEAT EXCHANGER, AND MEANS RESPONSIVE TOTHE OUTPUT OF SAID FIRST RESPONSIVE MEANS FOR TERMINATING THE OPERATINGOF THE DEFROSTING APPARATUS.